Launching the Mission:
When can vehicles be launched?
What method of propulsion will we use?
What will the launch vehicles carry?
How many launches will there be?
The orbits of Earth and Mars provide us with a 15 year trajectory cycle which is divided into 7 launch windows. Basically, about every 26 months a launch window presents itself and it is during this time that any spacecraft traveling to Mars must be launched. The Reference Mission begins with the first launch of Mars-crew support equipment in the year 2007. In each of the launch windows it is assumed that 3 successful launches are made to a common safe landing site where each mission will add to previously established infrastructure.
1) Propulsion for Inbound Mars Transit
Conventional chemical rockets (currently used for the space shuttle) will be used to launch Mars-bound spacecraft into LEO. The propulsion system that will most likely be used by the Mars transit vehicles once in LEO will be Nuclear Thermal Propulsion. Developed to near-flight status in the 1960s, for any given velocity change, a nuclear thermal rocket (NTR) uses about half as much propellant as a chemical engine. The liquid hydrogen NTR rocket will be used only after the spacecraft has left the Earth's atmosphere and adequate shielding will exist in the trans-Mars injection (TMI) stage of the transfer vehicle to protect the astronauts from radiation which will develop while the rockets are firing. The NTR will only be used on the outbound leg of the mission; the main benefit being the increased payload capability of such a rocket due to the dramatic reduction in required fuel for transit. Other theoretical and untested methods of propulsion exist, but only NTR technology is both feasible and significantly developed for use on a near-future mission.
2) Launch Schedule
The following launch schedule is intended for reference use only; none of these launches have approval or funding. Nonetheless, the sequence of launch events seen here can be applied starting in any of the 7 launch opportunities within any 15 year trajectory cycle.
A) The September 2007 Opportunity:
Launch 1 (Cargo) - A fully fueled Earth return vehicle (ERV) is delivered to Mars orbit on the minimum energy trajectory. The ERV will contain supplies for the crew on their return to Earth and it will be identical to the habitat used by the astronauts during their stay on, and their transit to, Mars. The ERV will also include an Earth re-entry capsule in which the crew will "splash down" into the ocean upon Earth return in much the same way as the astronauts of the Apollo missions.
Launch 2 (Cargo) - This launch will send mission critical equipment to the surface of Mars, also on the minimum energy trajectory. The payload will consist of an unfueled Mars ascent vehicle (MAV), a liquid oxygen/methane propellant production module, a 160 kW nuclear power module, a supply of liquid hydrogen (to be explained later), a utility truck, and a pressurized rover.
Launch 3 (Cargo) - Here a surface laboratory, a second 160 kW nuclear power module, a utility truck, tools, spare parts, and a remotely controlled rover will be delivered to the Mars surface via the minimum energy trajectory. The second nuclear power module will provide complete power system redundancy and, should it become necessary to use the laboratory module as an emergency shelter, the surface laboratory will contain non-perishable food supplies for the crew.
B) The October 2009 Opportunity:
Prior to launching further cargo missions or the crew, all surface equipment delivered during the 2007 launch window will need to be checked out. It must be confirmed that the previously delivered MAV is fully fueled and that all safety and mission critical systems check out. The ERV in Mars orbit must also be verified to be fully functional. If any of the crew safety or mission critical systems are not functioning properly, the crew launch will be postponed until those systems can be restored or replaced. System redundancy is crucial to the safety of the Mars astronauts; especially the MAV and the ERV systems.
Launch 1 (Cargo) - This launch is identical to the first launch of the 2007 opportunity. A second fully fueled ERV is delivered to Mars orbit on the minimum energy trajectory. This ERV will provide return vehicle redundancy for the first Mars crew and, if unused by the first Mars crew, this ERV will be used by the second Mars crew due to be launched in the window beginning late in 2011. Typically, the ERVs will remain untended for 4 years before they are used by a returning Mars crew.
Launch 2 (Cargo) - This launch will be similar to the second launch of the 2007 opportunity. A second unfueled MAV will be delivered along with a second liquid oxygen/methane propellant production module, more liquid hydrogen, scientific equipment, spare parts, and bioregenerative life support equipment. The second MAV provides system redundancy for the Mars crew in the event that the first MAV is somehow inoperable. The MAVs will generally be on the Mars surface for 4 years before use due to the ascent vehicle redundancy necessary to ensure the safe return of the astronauts. The bioregenerative life support equipment is not critical to mission success, but it will be a valuable experiment in life support system technology. It is hoped that a bioregenerative life support system could be used to produce small amounts of fresh food and also help to recycle air and water.
Launch 3 (First Mars Crew) - This will be the first crewed vehicle ever to make the journey to Mars. They will depart in mid-November of 2009 on the fast transit trajectory. The 2009 window is the "worst case" scenario in which the transit time to Mars will be about 180 days. By initiating the human Mars exploration program during the most difficult transit scenario, we will be well prepared for all future missions. The fast transit trajectory will put the astronauts in Mars orbit about 2 months before the arrival of the fourth and fifth cargo missions. If for some reason the astronauts are unable to land at the site of the previous cargo missions, the astronauts' transit module will contain all of the crew provisions needed for the 180 day transit as well as the 500-600 day surface stay (the arriving MAV could then be redirected to land nearby). The transit module will also serve as the main crew quarters during the astronauts' stay on Mars.
The first Mars crew will likely consist of 6 or 7 individuals who possess expertise in several disciplines. Some of the areas of knowledge that will be required by the crew will include: 1) maintenance, repair and operations of mechanical, electrical, and electronic devices 2) general medicine including surgery, psychology, and biomedicine 3) geology, geophysics, paleontology, geochemistry, and atmospheric science 4) biology, botany, ecology, and social science. In addition to these areas of expertise, all crew members will require extensive skills in management, communications, computer science, navigation, and journalism (a large part of the return on mission investment is the reporting of surface operations to the population of Earth).
C) The December 2011 Opportunity: & D) The March 2014 Opportunity:
The next two launch windows will closely mirror the 2009 launch opportunity. Each window will consist of two cargo launches followed by one crewed vehicle. The equipment carried by the cargo missions will depend upon several factors: 1) the suggestions made by the first crew 2) required spare parts 3) status of surface systems (ie. system redundancy must be maintained) 4) scientific objectives (these are likely to change as the mission proceeds).
While they will be similar to the 2009 mission, it would be impossible to predict the exact structure of the 2011 and 2014 Mars missions. Unforeseen developments on the Martian surface, as well as developments here on Earth, will certainly alter the course of human Mars exploration to some degree. One thing that is for certain is the fact that the 2011 and 2014 missions will build on the infrastructure and scientific achievements of the mission(s) before them. Over the course of the total of 12 launches from Earth, significant amounts of equipment will accumulate at the landing site and Mars surface operations experience will be continually developed. Our expanding knowledge of Mars as a planet will lead us is new directions of exploration, on Mars and on Earth, and perhaps a second Mars landing site will be selected for future investigation. The experience gained from previous Mars missions will streamline the process of "outpost" establishment significantly and advances in technology will make Mars increasingly accessible to astronauts. As old questions are answered and new ones are raised, we will be well on our way to establishing a future in which we step out into the stars in search of answers. As one can imagine, a human Mars exploration program spanning only 9 years would certainly provide significant returns.
Why Go to Mars? - motivations behind a human Mars exploration program
Mission Objectives and Profiles - objectives, risk evaluation, trajectories, travel/stay times, split mission strategy
Landing on the Martian Surface - entry & landing, surface equipment, surface operations
Surface Systems - power, return propellant production, surface life support
Return to Earth - ascent from the Mars surface, Earth Return Vehicle
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